A variety of different kinds of surface coverings, in particular floor, ceiling or wall coverings are known in the art. In particular for interior applications, wooden panels or panels having the appearance of wood are very popular. In the recent years laminate panels have been developed in particular to be used as flooring panels reproducing the appearance of various kinds of different wood panels.
In general, laminate panels comprise a base or carrier board of MDF, HDF or OSB which is provided on one side with a decor for example to reproduce the appearance of a real wood panel. This decor can be provided either as a printed paper layer or a veneer, or the decor can be directly printed onto the carrier board. Often, these panels are of rectangular shape and can be coupled to each other using complementary coupling means which commonly are formed as integral parts at the panel edges. Thus, similar panels can be connected at corresponding adjacent edges to form for example a floor covering. Among these coupling means in particular various kinds of tongue and groove based coupling means are known which allow for form fitting connections between similar panels by introducing the tongue of one panel into the groove of another panel. To lock the panels together in horizontal and vertical directions, the coupling means are further provided with suitable locking elements, which allow the panels to be firmly locked to each other. Thereby it is possible that such tongue and groove coupling means with additional locking elements can lock respective coupled panels perpendicular to their common connection joint as well as perpendicular and parallel to the panel plane without the need for additional locking means such as for example glue.
In the case of rectangular panels, it is common that panels are provided with two different kinds of coupling means. For example, two opposing longitudinal edges of such panels can be provided with tongue and groove coupling means, which allow similar panels to be connected to each other at adjacent longitudinal edges by angling. In this case, the transverse opposing edges of these panels can be provided with coupling means which allow similar panels to be connectable to each other at adjacent transverse edges by vertical folding. This combination of coupling means allows that a panel can be connected to a row of similar panels by angling this panel around corresponding longitudinal adjacent panel edges, while within the same working step this panel is connected to neighbouring panels by vertical folding to corresponding adjacent transverse panel edges.
An example of such a tongue and groove coupling mechanism is described in the German patent application DE 199 29 896 A1. The DE'896 describes panels which are provided at opposing transverse edges with coupling means which allow for coupling of panels by vertical folding. The transverse coupling means described therein are hook-shaped coupling members which can be formed integrally with the transverse panel edges. Upon connection of the panels, these hook-shaped coupling members interlock, thereby coupling the panels perpendicular to the transverse panel connection joint and parallel to the panel plane. Each of these hook-shaped coupling members is provided with a locking element to provide a coupling of the panels also in a direction perpendicular to the panel plane. However, if the connection is subjected to pressure, e.g. when a person stands on the panel, it is still possible that panel edges and in particular the corners of connected panels are deflected downwards.
A further development of such coupling mechanisms is described in the WO 01/51732 A1. This document describes tongue and groove coupling means which are similar to the above described hook-shaped coupling members which can be provided on transverse edges of panels. Upon coupling of panels at corresponding transverse edges, a transverse tongue of one panel is inserted into a corresponding groove of another panel by vertical folding. To increase the stability of this connection, the WO'732 discloses to insert an extraneous locking element into a channel, which is formed by the transverse coupling means. To form this channel, a recess is provided in the transverse tongue which in coupled condition, when two panels are connected to each other, opposes a corresponding recess provided in an adjacent transverse groove. After coupling two panels, the extraneous locking element is inserted into this channel to lock the two panels in a direction perpendicular to their transverse edges and perpendicular to the panel plane.
Similar coupling mechanisms in which extraneous locking elements are used to lock the transverse edges of panels with each other are e.g. known from WO 2003/016654 A1 and WO 2007/079845 A1. All the known solutions have in common that they only provide a secure connection at the transverse sides, however, the corners of the connected panels cannot be locked thereby.
A generally known difficulty which can arise in the case of surface coverings consisting of panels as described above is instability at the interconnection zones where three connected panels met. The reason for that is that the corners of such panels, i.e. where longitudinal coupling means and transverse coupling means meet, are not provided with any coupling means for manufacturing reasons. Thereby, no tight locking occurs at these corners and the panel surface remains bendable in this area.
It is an object of the present invention to improve the state of the art by providing an improved surface covering with an improved way of coupling panels, as for example laminate panels for surface coverings. It is in particular a further object of the present invention to provide more reliable coupling means, which offer an improved interconnection at the corners of the panels. It is an even further object of the present invention to provide an improved extraneous locking element which facilitates the laying process and reduces the amount of deficient products.
These and other objects which become apparent upon reading the following description are solved by a surface covering according to claim 1 and an extraneous locking element according to claim 44.